This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:
3GPPthird generation partnership projectASCsubcarrier used for asynchronous signalingCDMcode division multiplexingCPcyclic prefixDLdownlink (eNB towards UE)eNBE-UTRAN Node B (evolved Node B)EPCevolved packet coreE-UTRANevolved UTRAN (LTE)FFTfast Fourier transformFIRfinite impulse responseFSUflexible spectrum useHARQhybrid automatic repeat requestI/Qinphase/quadratureICIintercarrier interferenceIFFTinverse fast Fourier transformISIintersymbol interferenceLTElong term evolution of 3GPPMACmedium access control (layer 2, L2)MIMOmultiple input multiple outputMM/MME mobility management/mobility management entityNCOnumerically controlled oscillatorNode Bbase stationO&Moperations and maintenanceOFDMorthogonal frequency division multiplexOFDMAorthogonal frequency division multiple accessPDCPpacket data convergence protocolPHYphysical (layer 1, L1)RBresource blockRLCradio link controlRRCradio resource controlRRMradio resource managementS-GWserving gatewaySCsubcarrierSC-FDMAsingle carrier, frequency division multiple accessSNRsignal to noise ratioUEuser equipment, such as a mobile station or mobile terminalULuplink (UE towards eNB)UTRANuniversal terrestrial radio access network
The International Telecommunications Union (ITU) is specifying system requirements for next generation mobile communication systems, referred to at present as International Mobile Telecommunications-Advanced (IMT-A). Current 3 G mobile communication systems, including their evolutions, are in this respect part of the ITU IMT-2000 system. IMT-A systems are expected to provide peak data rates in the order of 1 Gbit/s in local areas (LAs). To support these data rates advanced MIMO antenna technology will be used in order to achieve high spectral efficiency. In addition, a high system bandwidth allocation, in the range of about 100 MHz, is expected to be used.
Even though new frequency bands are expected to be allocated for use by IMT-A, the high system bandwidth requirements will require that different system operators share the available spectrum. This presents a radically different approach to that used currently in IMT-2000 systems (e.g., GSM/UMTS), where each network operator operates its associated network in a dedicated licensed band. The spectrum sharing may be referred to generally as FSU.
One challenge in the use of FSU is determining at a particular device A whether a given spectrum resource may be safely used without interfering with the reception of device B. More specifically, even though device A cannot directly sense a transmission that device B receives, it will cause undue interference in the reception of that transmission if it uses the same portion of the spectrum resource for its own transmission.
A number of state-of-the-art communication systems use frequency domain processing. In such a system, the total transmit bandwidth is divided into a number of subcarriers, separated by frequency intervals that are proportional to the inverse of the symbol length. The spectrum of each individual subcarrier contains spectral nulls at the frequencies of all other subcarriers, allowing a low-complexity implementation of both the receiver and transmitter. The addition of a cyclic prefix (CP) allows the receiver to process one symbol at a time, even though the timing between transmitter and receiver may be known only with limited accuracy and is possibly blurred by multipath reflections. Since OFDM is a well-known system using frequency-domain processing, such radio systems that use frequency domain processing will be referred to herein for convenience, and not as a limitation, as “OFDM-like systems”. SC-FDMA is an example of another “OFDM-like” system. Typically, frequency domain processing is implemented in receivers and transmitters using FFT and IFFT to convert signal representations between the time domain and the frequency domain.
In OFDM-like systems a possible approach is to enable signaling between nearby nodes by allocating subcarriers for signaling between unsynchronized devices. Such subcarriers will be referred to as ASCs (“asynchronous subcarriers”). A radio system may use any number of ASCs for FSU coordination and for other purposes. For example, a radio system may group 12 subcarriers into one resource block (RB), and allocate one ASC per resource block. The resulting spacing of 180 kHz between ASCs provides robustness against frequency selective fading.
If devices are synchronized, a message broadcast on ASCs would not interfere with reception of other devices on nearby subcarriers. However, when the transmitter and receiver are unsynchronized one consequence may be the generation of intercarrier interference (ICI) into nearby subcarriers, thereby deteriorating reception.
In a publication “Dual Busy Tone Multiple Access (DBTMA) B A Multiple Access Control Scheme for Ad Hoc Networks”, Z. Haas et al., IEEE Transactions on Communications, Vol. 50, No. 6, June 2002, there is described a coordination mechanism that uses narrow-bandwidth, out-of-band tones.
The concept of adding “training”/“pilot” signals specifically for asynchronous OFDM reception is generally known, as indicated by a publication “Source separation of asynchronous OFDM signals using superimposed training”, V. Venkateswaran et al., ICASSP 2007. This publication proposes to provide a “superimposed training sequence”. However, the sequence appears to be padded with a CP.
The technical specification 3 GPP TS 36.211 V8.3.0 (2008-05), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8) describes the physical channel and modulation processing requirements in radio transmitters and receivers according to E-UTRA (evolved UTRA, also known as LTE (long term evolution)).